Wagner N. Mussel

Preparation and characterization of Nickel-and cobalt-doped magnetites

Nickel- and cobalt-doped magnetites were prepared by a co-precipitation method and studied in some detail, in an effort to identify some effects of the doping cations on the magnetic, crystallographic and morphological properties of the resulting spinel. The synthetic samples were characterized by conventional chemical analysis, powder X-ray diffractometry, Mossbauer spectroscopy, saturation magnetization and scanning electron microscopy. From chemical analysis, the continuous increase of Ni2+ or Co2+ is accompanied by a simultaneous decrease of the Fe2+ contents, in the spinel structure. The magnetization values also decrease continuously with increasing doping cation contents. Mossbauer parameters are characteristic of substituted magnetites and indicate the presence of a single phase only. Based on the inverted intensities of the lines 1 (leftmost, on the negative Doppler velocity scale) and 2 of Mossbauer spectra of doped samples, relatively to the pure magnetite, it was assumed that the isomorphical substitution occurs preferentially on octahedral coordination sites of the spinel structure. The coercive field of these ferrites decrease steadily with Ni2+ but increases with Co2+ contents, reaching a maximum at x = 0.38, in the general formula CoxFe3-xO4 .

ANÁLISE TÉRMICA APLICADA À CARACTERIZAÇÃO DA SINVASTATINA EM FORMULAÇÕES FARMACÊUTICAS

Thermogravimetry (TG) and differential scanning calorimetry (DSC) are used in pharmaceutical studies for drugs characterization, purity, formulations compatibility, polymorphism identification, stability evaluation, and thermal decomposition of drugs and pharmaceutical formulations. Simvastatin showed fusion at 138.5 oC and thermal stability up to 248 oC. Simvastatin was incompatible with preservative excipient butylhydroxyanisole (BHA) performing a process of crystal amorphization. The drug showed morphological polymorphism, where it has the same unit cell but with different crystal habits according to the recrystallization solvent.

Pentacyclic triterpenes from branches of Maytenus robusta and in vitro cytotoxic property against 4T1 cancer cells

Dois novos friedelanos, 1 e 2, e cinco triterpenos pentaciclicos conhecidos foram isolados dos galhos de Maytenus robusta. Suas estruturas quimicas foram identificadas como 3,16-dioxo-29hidroxifriedelano (1), 3-oxo-16b,29-di-hidroxifriedelano (2), 3-oxofriedelano (3), 3b-friedelinol (4), 3,16-dioxofriedelano (5), 3-oxo-29-hidroxifriedelano (6) e 3,16-dioxo-12a-hidroxifriedelano (7). A estrutura e estereoquimica dos triterpenos 1 e 2 foram estabelecidas por infravermelho (IR), ressonância magnetica nuclear (NMR) 1D/2D, espectrometria de massas de alta resolucao com ionizacao quimica a pressao atmosferica (HR-APCIMS) e difracao de raios X de po. A atividade citotoxica in vitro dos triterpenos 1 a 6 foi avaliada frente a celulas de câncer de mama murino. Os triterpenos 1 e 2 apresentaram atividade citotoxica contra celulas 4T1 em baixa concentracao. Two new friedelane-type compounds 1 and 2 and five known pentacyclic triterpenes were isolated from branches of Maytenus robusta. Their structures were identified as 3,16-dioxo29-hydroxyfriedelane (1), 3-oxo-16b,29-dihydroxyfriedelane (2), 3-oxofriedelane (3), 3b-friedelinol (4), 3,16-dioxofriedelane (5), 3-oxo-29-hydroxyfriedelane (6), and 3,16-dioxo12a-hydroxyfriedelane (7). The structures and the stereochemistry of triterpenes 1 and 2 were established through infrared (IR), 1D/2D nuclear magnetic resonance (NMR), high-resolution atmospheric pressure chemical ionization mass spectrometry (HR-APCIMS) spectral data and powder X-ray diffraction. The in vitro cytotoxic property of triterpenes 1 to 6 on 4T1 murine breast cancer cells was evaluated. The triterpenes 1 and 2 showed cytotoxic activity against 4T1 cells at a lower concentration.

Chemical interactions study of antiretroviral drugs efavirenz and lamivudine concerning the development of stable fixed-dose combination formulations for AIDS treatment

Lamivudine and efavirenz are among the most worldwide used drugs for acquired immune deficiency syndrome (AIDS) treatment. Solid state nuclear magnetic resonance (ssNMR), Fourier-transformed infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermo-optical analysis (TOA) were used to study possible interactions between these drugs, aiming the development of a fixed-dose drug combination. DSC and TOA have evidenced significant shifts on the melting points of both drugs in the mixture, which may be due to interaction between them. Although DSC and TOA results indicated incompatibility between the drugs, FTIR spectra were mostly unmodified due to overlapping peaks. The ssNMR analyses showed significant changes in chemical shifts values of the mixture when compared with spectra of pure drugs, especially in the signals relating to the deficient electron carbon atoms of both drugs. These results confirm the interactions suggested by DSC and TOA, which is probably due to acid-base interactions between electronegative and deficient electron atoms of both lamivudine and efavirenz.

Combined experimental powder X-ray diffraction and DFT data to obtain the lowest energy molecular conformation of friedelin

Friedelin molecular conformers were obtained by Density Functional Theory (DFT) and by ab initio structure determination from powder X-ray diffraction. Their conformers with the five rings in chair-chair-chair-boat-boat, and with all rings in chair, are energy degenerated in gas-phase according to DFT results. The powder diffraction data reveals that rings A, B and C of friedelin are in chair, and rings D and E in boat-boat, conformation. The high correlation values among powder diffraction data, DFT and reported single-crystal data indicate that the use of conventional X-ray diffractometer can be applied in routine laboratory analysis in the absence of a single-crystal diffractometer.

Kinetic study of anti-HIV drugs by thermal decomposition analysis: A multilayer artificial neural network propose

Kinetic study by thermal decomposition of antiretroviral drugs, efavirenz (EFV) and lamivudine (3TC), usually present in the HIV cocktail, can be done by individual adjustment of the solid decomposition models. However, in some cases, unacceptable errors are found using this methodology. To circumvent this problem, here is proposed to use a multilayer perceptron neural network, with an appropriate algorithm, which constitutes a linearization of the network by setting weights between the input layer and the intermediate one and the use of kinetic models as activation functions of neurons in the hidden layer. The interconnection weights between that intermediate layer and output layer determine the contribution of each model in the overall fit of the experimental data. Thus, the decomposition is assumed to be a phenomenon that can occur following different kinetic processes. In investigated data, the kinetic thermal decomposition process was best described by R1 and D4 models for all temperatures to EFV and 3TC, respectively. The residual error of adjustment over the network is on average 103 times lower for EFV and 102 times lower for 3TC compared to the best individual kinetic model. These improvements in physical adjustment allow detailed study of the process and therefore a more accurate calculation of the kinetic parameters such as the activation energy and frequency factor. It was found

Compositional and structural variabilities of Mg-rich iron oxide spinels from tuffite

E_{\text{a}} = 75.230\,{\text{kJ}}\,{\text{mol}}^{ - 1}

Mössbauer hyperfine interactions in thermally treated iron-yttrium oxide systems

Ea=75.230kJmol-1 and